Discharge nozzles for propulsive jets



P. F. ASHWOOD DISCHARGE NOZZLES FOR PROPULSIVE JETS Filed June 3, 1957 FIG! 5 Sheets-Sheet 1 Nov. 5, 1963 P, F. AsHwooD 3,109,284

DISCHARGE NOZZLES FOR PROPULSIVE JETS F'iled June-'5, 195'? I7 5 Sheets-Sheet 2 Ncv. 5, 1963 P. F. AsHwooD 3,109,284

DISCHARGE NOZZLES FOR PROPULSIVE JETS Filed June 5, 1957 3 Sheets-Sheet 3 United States Patent O DISCHARGE NZZLES FOR PRDPULSEVE JETS Peter Frederick Ashwood, Farnham, England, assigner to Power `lets (Research and Development) Limited, London, England, a British company Filed .lune 3, 1957, Ser. No. 663,254 Claims priority, application Great Britain .inne 14, 1956 4 Claims. (Cl. 60-35.6)

This invention relates to discharge nozzles for propulsive jets. Iwo general forms of discharge nozzle coniiguration are known; these are firstly a nozzle of convergent configuration which operates at maximum efiiciency at a determined subsonic flight speed and secondly a nozzle of convergent-divergent conguration4 which operates at maximum efficiency at a determined supersonic flight speed. Proposals have been made for a nozzle of predetermined convergent divergent coniiguration which can be quickly converted to a predetermined convergent configuration.

In one such nozzle, as described in copending patent application Serial No. 549,028, now abandoned, a ventila-tion is provided in the region of the throat, so that `with the ventilation closed the nozzle can operate as a convergent-divergent nozzle while with the ventilation open it can operate as a convergent nozzle. The former condition will normally correspond to the maximum ight speed of the aircraft which will be supersonic while the latter condition corresponds to a particular subsonic ight speed. The efficiency of 4the nozzle will be at a maximum at these two flight speeds and will be somewhat reduced at intermediate Values. The intermediate flight speeds may however correspond to conditions in which high thrust is required, for example, to transonic flight speeds in the approximate Mach number range of 0.9 to 1.2. The present invention has for an object the achievement of Iimproved nozzle eiciency at these intermediate flight speeds.

The present invention provides a discharge nozzle for a propulsive jet having iluid retaining tubular walls delining a flow path of convergent-divergent configuration, said walls comprising, in the direction of ilow, a convergent nozzle portion, a lirst divergent nozzle portion and a second divergent nozzle portion the upstream end of which is outwardly stepped from the downstream end of said rst divergent nozzle portion. By the expression outwardly stepped is meant the configuration which would be produced, in a conventional convergent-divergent nozzle having a smoothly continuous wall, if an annular portion of the divergent part of the nozzle were removed and the remaining portion downstream thereof were moved in the upstream direction.

Between the said divergent nozzle portions, a peripherally extending ventilation slot may be formed through which -uid can enter the flow path. Thus the region of said ventilation slot is preceded in the direction of fluid ow by a part of the flow path which is at least slightly divergent. With the said ventilation slot open and in the absence of any other ventilation slot the performance of the nozzle approaches that of a convergent-divergent nozzle with a slight amount of divergence. The nozzle will reach its maximum etiiciency at its maximum supersonic flight speed, i.e., with the ventilation slot closed, as in the case of a nozzle with ventilation at the throat, and also at a lower ght speed when the ventilation is open. This latter speed however will be higher than the lower speed at which maximum efciency :is achieved in the case of a nozzle ventilated at the throat, and the intermediate range of ight speeds over which eiciency is reduced is accordingly narrowed.

The use of the nozzle in a ventilated condition for aircraft propulsion at generally subsonic llight speeds in-` ice volves some loss of performance compared ywith a nozzle with ventilation only at the throat. Even so, at subsonic flight speeds it is still very much preferable to an equivalent unventilated convergent-divergent nozzle of lixed geometry. Moreover the comparative loss of performance noted is offset by a comparative improvement in performance when the nozzle according to the invention is used in the said ventilated condition for aircraft propulsion at for example transonic llight speeds, that is when the flight speed is in the approximate Mach number range of 0.9 to 1.2. Since a peak in the drag of an aircraft is encountered within this transonic speed range, the possibility aiforded by the invention of improved performance of the propulsion nozzle in that speed range is most advantageous. Conveniently therefore the nozzle is used in the ventilated condition for take-olf, and flight at subsonic and transonic speeds. Towards the end of the transonic speed range the nozzle is changed to a unventilated condition tor ight at higher speeds.

With a nozzle having a ventilation downstream of the throat, there is less tendency for constriction of the throat and consequent disturbance of the engine operating conditions to occur when the ventilation slot is open than in the case of a nozzle ventilated at the throat.

ln the absence of provision for ventilation at another region of the nozzle, the region of the said ventilation is at a location where the cross-sectional area of the nozzle is between 30% and 45% greater than the corresponding area of the nozzle throat. However provision may be made for the occasional ventilation of the flow path by communication `with the ambient liuid outside the nozzle in at least one further region of the nozzle located between vthe throat and the nozzle outlet. Thus provision for additional ventilation may be afforded at the region of the throat or at a second region downstream of the throat spaced in the direction of the flow from the first region.` Where provision for ventilation is thus afforded at two or more regions of the nozzle, the limits stated above in relation to a single ventilation slot need not apply and one of the regions of ventilation may be located nearer to the nozzle outlet than isimplie'd by those limits. Similarly the use of the nozzle would be modified. For instance, if the regions of ventilation (numbering say two) are located one at the 'throat of the nozzle and one downstream thereof, then the former or both ventilation slots may be opened during take-off and ight speeds up to the transonic range. ln the transonic range the throat ventilation slot is closed and the other opened, while at higher speeds both are closed. lf, for example, two regions of ventilation are spaced at intermediate points along the divergent part of the nozzle flow path then that nearest the throat or both may be open during take-oli and at flight speeds up to some intermediate transonic speed. For higher transonic speeds only the ventilation slot nearest the outlet remains open, while for higher speeds both are closed.

The ventilation may be controlled by closure means such as a movable valve or sealing ring externally embracing the nozzle in the region of the ventilation slot or a casing integral with the nozzle and enclosing that region which has apertures controlled by the ring. Alternaclose the ventilation slot or hole between them.

`In the accompanying drawings:

`FIGURE. l is a longitudinal sectional view of a gas turbine jet propulsion'engne having a convergent-divergent propulsion nozzle ventilated at three positions along its length,

FIGURE 2 isan enlarged View of a convergent-divergent nozzle showing in greater detail a nozzle similar to that of FIGURE l, but having ventilation at only one position,

FIGURE 3 is a transverse sectional view of the nozzle of FIGURE 2 'taken on the line 'III--IIL FIGURE 4 is an enlarged sectional view of part of the operating mechanism shown in FIGURE 2,

FIGURES and 6, show two alternative forms of ventilated convergent-divergent nozzle.

Thegas turbine engine shown in FIGURE 1 has a compressor 1 receiving air from atmosphere and delivering pressurised air to a conventional combustion system and turbine (not shown) the latter driving the compressor. The exhaust gases from the turbine pass to an outlet duct 2 of circular cross-section which encloses bales 3 of an after-burning or reheating system. The outlet duct terminates in a nozzle 4 and together with the latter is enclosed in a circumferential casing 5 to which air is admitted. The nozzle has a llow path of convergent-divergent configuration which, as shown by Way of example, is ventilated at three locations 4a, 4b, 4c, the first at the nozzle throat and the further two along its divergent portion.

FIGURE 2 shows on an enlarged scale a nozzle of convergent-divergent configuration which comprises three frusto-conical wall members of sheet metal disposed on a common axis. The first or entry member 8 is attached to the outlet end of the duct 2 and converges downstream therefrom to a nozzle throat 11, second or intermediate member 9 is attached at its upstream end to the downstream end of the rst member 8 and diverges downstream therefrom and the third or discharge member 10 is located with its upstream end adjacent to the downstream end of the member 9 and diverges downstream therefrom. The upstream end of the member 10 has a diameter Vgreater by about 10% than the diameter of the adjacent end of the member 9 and is spaced axially therefrom by a distance equal to about 8% of the diameter of said adjacent end. Thus the internal prole of the nozzle is of generally convergent-divergent form but is discontinuous, having an outward step at an intermediate point on the divergent part of the profile, which step affords an annular ventilation slot 12 in the fluid retaining walls of the nozzle. The location of the slot is such that the downstream end of the member 9 which defines the upstream limit of the slot has an internal area which is say 40% greater than the area of the nozzle throat, the value being in general between 30% and 45% greater than the throat area. The downstream end of the member 10 may have an area between 100% and 170%, say 115% more than the throat.

The wall members are connected by a number of beams 14, for example six, spaced evenly around the nozzle axis and each attached externally to the wall members 9 and 10 and two radially upstanding circumferential llanges 15, 16 are secured one to each of the wall members 9 and 10 and spaced in each case away from the adjacent ends thereof. A number of, for example, three, guide rods 17 are spaced evenly around the nozzle, and each extends axially between and through these flanges, being retained against axial movement by means (not shown), for example, Vwashers bearing on the anges and held by split pins through the rods. The wall member 9 has near its downstream end a radially upstanding circumferential seating llange 18 and corresponding seating flange 19 surrounds the upstream end of the wall member 10 being spaced radially from that member and axially from the seating flange 18. The seating flange 19 is connectedby an axially extending bellows 20'to Ythe exterior surface of the wall member 10. The peripheries of the two seating flanges are formed to provide seating surfaces in a common conical envelope converging in' the upstream direction. A closure ring 21 consisting of two semi-circular halves bolted together surrounds the nozzle, the guide rods passing through holes 22 in the ring so that the latter is slidable axially on the Y the communication between the ventilation slot 12 and' guide rods 17. The closure ring has an internal conical seating surface corresponding to those on the seating flanges. The arrangement is such that the ring in one position engages the two seating ilanges to define therewith a chamber 23 enclosing the ventilation slot and is movable in the upstream direction to disengage the seating llanges and so open avent to place the slot in communication with ambient air surrounding the nozzle. The flexible mounting of the seating flange 19 provided by the bellows 20 promotes the effectiveness of the seating of the ring since the seating flange may yield axially when the ring is seated and so compensate for differential Y the nozzle with their axes extending parallelto the'axis of the nozzle. They are attached respectively tothe wall member 9 and to the closure ring 21 and operate to move the latter along the guide rods to open or close atmosphere as the Mach number of the flight speed is decreased or increased respectively. The jacks and guide rods may conveniently be disposed in alternating stations mid way between successive pairs of beams 14. The means for operating the jacks include a servo-mechanism 28 responsive to a pressure ratio or pressure difference which is conveniently determined by the pressure of' lluid entering the nozzle and the ambient atmospheric pressure at the nozzle outlet.

As is shown in detail in FIGURE 4 the servo-mechanism 28 comprises a dumbell piston valve 30 with afixed cylinder 31 having a central inlet 32 connected to a supply (not shown) of pressurised servo fluid. The cylinder has two outlets 33, 34 spaced on either side of the inlet by a distance corresponding to the spacing of theY en-V larged ends of the piston valve, which outlets are connected to each jacks on opposite sides of the actuating piston 26 thereof. Two exhaustports 35, 36 are provided in the valve cylinder spaced outwardly of each outlet. The piston valve has a connecting rod 37 extending into a low pressure chamber 38 attached to -the valve cylinder and constituting part of a pressure responsive device. The connecting rod is attached to one end of an evacuated bellows 40 which has its other end attached to the wall of the low pressure chamber. pivoted lever 41 mounted within and supported from va wall of this chamber and extending at right angles tothe piston rod has a stirrup connection 42 at one end with a spigot 43 on the connecting rod. The other end of the lever has a similar stirrup connection 44 with a spigoty 45 on an actuating rod 46 which rod extends parallel to the connecting rod. The actuating rod 46 projects from a flexible diaphragm 47 dividingthe low pressure charnber from a high pressure chamber 48. Adjusting screws 49, 50 in the high and low pressure chambers limit the movement of the diaphragm in the direction along the actuating rod. The high and low pressure chambers,Y

have connections to high and low pressure sensing means 53, 54 appropriate to the control desired; as shown in FIGURE 2 the high pressure chamber is connected to the end of the duct immediately upstream of the nozzle and the low pressure chamber is connected to the static pressure of the ambient air outside the nozzle. The mechanism can be so adjusted that the actuating rod, lever and the connecting rod and piston move to operate the jacks when the pressure ratio across the diaphragm exceeds or falls below a particular value. Alternatively the pressure responsive device may actuate a microswitch which in turn operates the piston valve, in which case the connecting rod is connected to a plunger operating a micro-switch and the latter is connected in seriesA with a solenoid, the solenoid armature being connected above.

In an alternative nozzle construction shown in FIG- URE 5 the nozzle has iluid retaining wall members, 9,

A Ycentrally In another constructional embodiment shown in FIG.

6 the nozzle has ilu-id retaining wall members 8, 9, 10 as in the embodiment previously described and an extension of the fluid duct 2 forming a casing `65 overlapping the nozzle. In this case wall member of .the nozzle is attached not directly to this casing but to a sleeve 66 which slides telescopically within the casing, so that the wall member 10 yof the nozzle can move axially towards and away lfrom the remainder of the nozzle. The intermediate wall member 9 has a seating 67 Iformed near its downstream end and the upstream end of the wall member 10 can move to engage this seating and close theV ventilation slot. The casing has apertures `68 which are in communication with the ventilation slot when the latter is open, but which are closed by the sleeve r66 when the slot -is closed. Axially extending jacks 25 are attached to the casing 65 and discharge member 10 `and operate to move the latter axially, the jacks bein-g controlled by means as in the embodiment first described.

Each of the constructions described above may be modied, lin accordance with copending patent application Serial No. 598,344 by providing in the region of the throat of the nozzle -a circumferential injection slot for pressurised fluid. Thus an external chamber is provided circumferentially enveloping the injection slot or, where the structure includes a cylindrical casing, a partition may extend between the `casing and nozzle wall to form such a chamber. The chamber has one or more external connections to a source of pressurised fluid, for example, the compressor of the -jet engine. yEach connection has a iiu-id valve controlling the supply of press-urised fluid. By admission of this fluid tothe injection slot the effective throat area `of the nozzle may be reduced. Alternatively, and aga-in in accordance with the copending patent application mentioned above, a similar effect may be aforded by the provision in each of the above constructions of a circumferential recess in the nozzle wall in the region of the throat and a pair yof semi-circular Varms housed in the recess. The arms are each pivoted near one pair of their adjacent ends about an axially extending axis. The adjacent free end of the arms can move towards `or away from vone another so that the arms lie completely within the recess in an inoperative position, or may protrude into the flow path to restrict the throat `area `of the nozzle. Lugs are provided near the free ends of the arms which lugs extend through the wall of the recess and afford connections -for actuating means. The free ends may overlap somewhat to oppose leakage from the nozzle.

A further constructional embodiment has intermediate and discharge lwall members similar to those of the embodiment first described. The nozzle further includes a convergent entry Iwall member which has its convergent downstream end, which defines the nozzle throat, spaced axially yfrom the upstream end of the intermediate member by a dist-ance equal to about 8 percent of the throat diameter. The diameter of the upstream end of the intermediate member is about r10 percent greater than the throat diameter. Thus there is a second ventilation slot associated with an outward step in the nozzle ow path at the throat of the nozzle. The three -wall members are connected by axially extend-ing beams and circumferential locating flanges on the entry and discharge members serve to locate guide rods as in the embodiment firs-t described. Each ventilation slot has seating anges, a closure ring and actuating beams therefore as in the embodiment first described, each closure ring sliding axially on the common guide rods. The pressure responsive devices for each ring may be adjusted to operate differentially and in particular so that the device controlling the ventilation slot at the throat responds to a lower pressure ratio than the other device.

v The construction last desoribedmay be modified in any way mentioned in relation to the embodiment first described, but in the application thereto of means for constnicting the effective throat area of the nozzle, the injection slot -for pressur-ised fluid or recess for constrictor arms is located slightly upstream of the throat.

Another constructional embodiment of the invention is generally similar to the embodiment vfirst described but the entry portion of the nozzle is not attached to the intermediate member. Instead there is interposed between these two a constrictor or conventional construction asv commonly used to vary the outlet area of a convengent nozzle and referred to generally as an iris type of constrictor. A common `form has for example peripherally successiveintenleaved members extending downstream of the .nozzle wall and hinged thereto near their upstream ends. lLevers attached to each member are simultaneously actuated e.'g. by rotation of a tooth ring embracing the nozzle, Vto vary the orifice. Such a constrictor is mounted o-n the downstream end of the convengent entry portion of the nozzle now described. The downstream end of the interleaved members are adapted to extend in one position to meet the upstream end of the intermediate member to `form a continuous ilow path. In ano-ther position, the interleaved members are retracted inwardly to restrict the nozzle area at .their end to a minimum area defining the nozzle throat. At the same time an annular Ventilating slot is lformed round the retracted members which slot is associated with an outer step in the profile of the ow path. in the inner position the interleaved members will be convergent in the direct-ion of fiow and in their outer position they may be less convergent or even divergent.

I claim:

1. A jet discharge nozzle for propelling an aircraft hav- 'mg duid-retaining tubular walls defining a flow path l through said nozzle of convergent-divergent configuration said walls comprising, in the direction of flow, a convengent nozzle portion, a throat portion, a first wholly divergent nozzle portion and a second whoily divergent portion; the first and second 'wholly divergent nozzle portionshaving adjacent, respective `downstream and upstream ends, said ends being spaced apart in the direction of flow to define a peripheral uninterrupted apenture and of which said upstream end of said second wholly divergent portion is transversely enlarged with respect to the said downstream end of said first wholly divergent portion to form between said first and second wholly divergent nozzle portions an outward step in the direction of allow, the tirst and second divergent nozzle portions corresponding to axial cross-sections of coaxial frusto-conical surfaces with the apex of the second nozzle portion spaced upstream from the apex of the first nozzle portion, whereby air from outside said divergent nozzle portions can enter the ilo-w path and breakaway yfrom the wall of the second divergent nozzle portion is effected and means for closing said aperture.

2. A jet discharge nozzle tor propelling an aircraft over -a range of speeds -from subsonic to supersonic, the nozzle having Ifluid-retaining ltubular walls defining a flow path through the nozzle, the walls comprising, in the [direction of fiow, a convergent nozzle portion, a throat portion, a throat portion, a iirst wholly divergent nozzle portion and a second wholly divergent nozzle portion, fthe first and second wholly divergent nozzle portions having their adjacent, respective, downstream and upstream ends spaced apart in the direction yof flow to define a peripherally continuous laperture and of which the upstream end of the second nozzle portion is transversely enlarged with respect to the adjacent end of the iirst wholly divergent portion, the rst and second divergent nozzle portions having axial cross-sections of coaxial Ktruste-conical surfaces with the apex of the second nozzle portion spaced upstream from the apex of the first nozzle portion, thereby to define an outward step in Ithe direction |of ow whereby ambient air can pass into said ow path and means #for varying the configuration of flow Within said flow path according to aircraft speed, comprising means `for closing the aperture at the supersonic speed lrange of .the aircraft toy givea convergent-divergent dow and yfor opening the aperture at subsonic' and transonic speed ranges to Agive peripherailly uninterrupted break-away of the flow and a consequential convergent flow path followed by a degree of divergence.

3. A jet discharge nozzle ias claimed in claim 2 in which the downstream end of the r-st divergent nozzle portion idenes a ow path, the cross sectional area, transverse to the direction of ow, of which is about 30% greater than the corresponding area of the throat por; tion.

4. A jet discharge nozzle as claimed in claim 2 having means dening a further peripheral continuous aperture in the tubular Walls at the throat portion thereof.

References Cited in the file of this patent NACA Research Memorandum E52I27, Preliminary n Investigation of a Perforated Axia'lly Symmetric Nozzle 20 for Varying Nozzle lPressure Ratios, by Reshotko, Jan.

UNITED STATES PATENTS lPrice Nov. 8, 1949 Lee Aug. 11, 1953 Hausmann July 23, 1957 Philpot Aug. 25, 1959 Bertin et al. Aug. 23, 1960 FOREIGN PATENTS France Mar. 1l, 1953 France Sept. 28, 1955 Germany Nov. 23, 1953 Great Britain Apr. 29, 1949 Great Britain .lune 13, k1951 Great Britain June 22, 1955 OTHER REFERENCES 14, 1953; declassied Oct. 14, 11955.

Aircraft and Missile Propulsion, by Zucrow, copyright 1958, by John Wiley & Sons, pages 364-373.

Flow Separation in Overexpanding Supersonic Ex- 

1. A JET DISCHARGE NOZZLE FOR PROPELLING AN AIRCRAFT HAVING FLUID-RETAINING TUBULAR WALLS DEFINING A FLOW PATH THROUGH SAID NOZZLE OF CONVERGENT-DIVERGENT CONFIGURATION SAID WALLS COMPRISING, IN THE DIRECTION OF FLOW, A CONVERGENT NOZZLE PORTION, A THROAT PORTION, A FIRST WHOLLY DIVERGENT NOZZLE PORTION AND A SECOND WHOLLY DIVERGENT PORTION; THE FIRST AND SECOND WHOLLY DIVERGENT NOZZLE PORTIONS HAVING ADJACENT, RESPECTIVE DOWNSTREAM AND UPSTREAM ENDS, SAID ENDS BEING SPACED APART IN THE DIRECTION OF FLOW TO DEFINE A PERIPHERAL UNINTERRUPTED APERTURE AND OF WHICH SAID UPSTREAM END OF SAID SECOND WHOLLY DIVERGENT PORTION IS TRANSVERSELY ENLARGED WITH RESPECT TO THE SAID DOWNSTREAM END OF SAID FIRST WHOLLY DIVERGENT PORTION TO FORM BETWEEN SAID FIRST AND SECOND WHOLLY DIVERGENT NOZZLE PORTIONS AN OUTWARD STEP IN THE DIRECTION OF FLOW, THE FIRST AND SECOND DIVERGENT NOZZLE PORTIONS CORRESPONDING TO AXIAL CROSS-SECTIONS OF COAXIAL FRUSTO-CONICAL SURFACES WITH THE APEX OF THE SECOND NOZZLE PORTION SPACED UPSTREAM FROM THE APEX OF THE FIRST NOZZLE PORTION, WHEREBY AIR FROM OUTSIDE SAID DIVERGENT NOZZLE PORTIONS CAN ENTER THE FLOW PATH AND BREAKAWAY FROM THE WALL OF THE SECOND DIVERGENT NOZZLE PORTION IS EFFECTED AND MEANS FOR CLOSING SAID APERTURE. 